1. Field of the Invention
The present invention is broadly concerned with particulate metal oxide compositions having stabilized on the particulate surface reactive atoms selected from the group consisting of atoms of the halogens and Group IA metals. Preferred particulate metal oxides include nanocrystalline MgO and CaO, with average crystallite sizes of up to about 20 nm. In one embodiment, potassium atoms are stabilized on the surface of nanocrystalline MgO at a loading of from about 10-40% by weight potassium based on the total weight of the K/MgO composite, thus forming superbases useful for isomerizing and alkylating unsaturated species. In another embodiment, chlorine atoms are stabilized on the surface of nanocrystalline MgO thus forming a composition which is capable of halogenating compounds in the absence of UV light and elevated temperatures, as well as providing a non-water utilizing source of chlorine for bleaching purposes.
2. Description of the Prior Art
Nanocrystalline metal oxides having an average crystallite size of up to about 20 nm are known to possess surface reactivities and adsorptive powers which are considerably higher than typically available metal oxide samples. It is believed that the enhanced surface reactivities of these nanocrystalline metal oxides are due to morphological features of the small crystallites, such as the higher population of reactive surface sites at edges and corners, and at sites with ion vacancies. The small sizes and unusual shapes of the crystallites provide high ratios of edge/corner ions to total surface ions. The presence of these edge/corner sites and other reactive defect sites (such as vacancies) allow these materials to possess surprisingly high surface concentrations of reactive surface ions. For example, an edge or corner O.sup.2- anion is coordinatively unsaturated and is "seeking" Lewis acids to help stabilize and delocalize its negative charge. Conversely, an Mg.sup.2+ ion on an edge or corner site is "seeking" Lewis bases to stabilize and delocalize its positive charge. Therefore, these coordinatively unsaturated O.sup.2- and Mg.sup.2+ readily accept incoming reagents with Lewis base or Lewis acid characteristics.
Solid superbases (as used hereinafter, bases which are strong enough to extract a proton from toluene) are generally created when metal oxides are treated with alkali metals. These materials are capable of acting as catalysts for the isomerization of alkenes at room temperature. However, they are only capable of alkylation reactions at high reaction temperatures (i.e., 150.degree. C. or greater), and even then only for certain types of alkylations. These drawbacks result from the inability to achieve sufficiently high loadings of the alkali metal in the form of dissociated metal ions and electrons on the metal oxide surfaces. That is, in order to create superbases with enhanced alkylation abilities, higher and heretofore unobtainable alkali metal loadings are required.
Halogens exist as stable diatomic molecules unless contacted with an oxidizable compound. To halogenate a molecule, it is first necessary to dissociate the diatomic molecule into halogen atoms which are reactive. For example, if Cl.sub.2 is added to methane, no reaction will occur because the diatomic chlorine is very stable and non-reactive. However, if UV light is added, or if the reaction is carried out at a temperature of about 300.degree. C., the Cl.sub.2 will dissociate into highly reactive chlorine atoms, thus chlorinating the methane or re-forming Cl.sub.2 if there is inadequate methane available for reaction. There are no methods in the prior art by which halogens can be stabilized in the form of reactive atoms, absent use of UV light or high reaction temperatures.
There is a need for superbase compounds with increased surface base site concentrations as well as stronger base sites which are capable of alkene isomerization and dimerizations, including propylene-ethylene conversion to pentenes and heptenes. Furthermore, there is a need in the art for processes by which halogens can be stabilized on metal oxide particles as reactive atoms without the need for UV light or high temperatures.